Remote radar indicating system



July 8, 1958 R b. E. KENYON 2,842,759

REMOTE RADAR INDICATING SYSTEM Filed Sept. 17, 1948 9 Sheets-Shes? 1 Pl/l SE'T/ME CONVERTER Rf REcE/VER ATTQRNEY n July 8, 1958 D. E. KENYQN 2,842,759 1 REMOTE RADAR INDIGATING sYsTx-:M

Filed sept. 17, 1948 l s sheets-sheef 2 ME. wm l .WY f T 9 Sheets-Sheet 5 July 8, 1958 D. E. KENYoN REMOTE RADAR INDICATING SYSTEM Filed Sepf. 17, 1948 July 8, 1958 D,` E, KENYON 2,842,759

REMOTE RADAR INDICATING SYSTEM A Tra/:wry

July s, 1958 D. E. KENYoN 2,842,759

REMOTE RADAR INDICATING SYSTEM Filed Sept. 17, 1948 9 Sheets-Sheet 6 TTOR/VE Y D. E. KENYON REMOTE RADAR INDICATING SYSTEM July 8, 1958 s sheets-sheet 7 Filed Sept. 17, 1948 www.

NNN

INV UV TOR. rDHV/D E. KEA/YON @ff/YW@ A TTORNE Y July 8, 1958 D. E. KENYoN REMOTE RADAR INDICATING SYSTEM Filed sept. 17, 1948 9 Sheets-Sheet 8 lr; N INVENTOR.

,Z4 wo E. /ffE/VYON ATTORNEY July 8, 1958 D. EL .KENYON REMOTE RADAR INDICATING SYSTEM Filed lse `of enemy war planes.

United States Patent REMOTE RADAR INDICATING SYSTEM David E. Kenyon, Huntington, N. Y., assigner to Sperry Rand Corporation, a corporation of Delaware Application September 17, 1948, Serial No. 49,723

6 Claims. (Cl. 343-6) This invention is a system for providing full land accurate indication of the positions of objects detected in the vicinity of a remotely located radar search'system. It particularly concerns such indication distant from the point of scanning independently of any direct connections between the radar scanning system and the indicating arrangement.

This application is a continuation in part of my prior U. S. applications Serial No. 710,781, tiled November 19, 1946, now Patent No. 2,736,007, and Serial No. 738,055, led March 29, 1947, now Patent No. 2,570,249 issued October 9, 1951.

lt has heretofore been proposed that data from numerous radar units located at selected points over a large region be supplied to a central station for collation, and for determination of overall positions and progress of movable objects. Such arrangements have been thought particularly desirable for tactical purposes where radar units are employed to Search for and detect the approach vsed for this purpose, including proposals for making permanent records forttransmission, e; g. via facsimile, and other proposals `involving employment of multiple pairs of transmission lines, with band width reduction .and sacrice of detail and picture quality, and with risk of loss of the data at the` central station in event of failure or altered characterestics of any transmission line.

Various systems have been de` The disadvantages of proposals of this sort are readily l apparent, in that` numerous relatively vulnerable signal .transfer links are required, and detail is sacriced through the multiple transfers. Movement of targets, as indicated by progress of the radar images across the presentation screen, is obscured` when various successive transfers or reproductions of the picture are made. t

The requirement of multiple transmission lines for substantially immediate transfer of the radar data is itself Aa very serious limitation, tying up communication facilit ties, and moreover, limiting the use of the remote indicating radar system to employment between iixed stations. t

It is an important object of the present invention to provide an improved remote radar data system, and in particular to provide such a system arranged to operate without any sacrifice of clarity and detail of the radar picture; and a further object is `to provide immediate and exact duplication remote from the radar scanning system of the picture produced in the local indicatorof the radar apparatus, or ofthe picture which would be produced if a local indicator of high quality were `employed at the radar station. Along this line, it is an important object to provide a remote indicating radar system suitable for duplication in a craft, such as an airplane or a boat, of the radar view of various craft in the vicinity of a selected vantage point. In` meeting this objective, it becomes possible to presentgin an lairplane 2,842,759 Patented July 8, 1958 picture of the ships and other craft and other energy reliecting objectssuch as buoys and wharves in the vicinity of a selected vantage point in a harbor.

Radar systems for airport traic control purposes pro viding plan position indication to aircraft in the vicinity of the airport, have been provided for air traffic control purposes; and similarly, plan position radar apparatus has been provided for harbor trafc supervision, an example of the latter being a system installed in the harbor at Liverpool, England, by Sperry Gyroscope Co. Ltd.` of England. lt is highly desirable that a simple arrangement be provided for accurately duplicating on craft in the vicinity of such airports and seaports,. the radar pictures as viewed from the selected fixed vantage points. lt is desirable, moreover, that the apparatus required in the craft be relativly simple, and that a single radio channel with good economy of frequency spectrum be made to sutce for the complete data transmission between the radar transmitting and receiving and scanning apparatus and the remote indicating apparatus.

lt is an object of the present invention to provide a remote radar transmission system suitable for these purposes, and taking into account these desiderata.

In the operation of a remote radar indicating system,

Y azimuth angular synchronization and range sweep synbe entirely free from mutual interference among these transmission elements.

lt is an object of this invention, then, to provide an arrangement for economically and efficiently communicating these elements entirely free from any interference p among the synchronization andvideo signals, and employing them in accurately reproducing the local radar picture.

` In accordance with the present invention, the azimuth angular data is passed through a link including a selsyn transmitter arranged to receive sinusoidal primary excitation and to provide a plurality of secondary output voltages, the relative magnitudes and polarities of theV secondary output voltages giving an unambiguous representation of instantaneous angular disposition of the radar `scanning unit. The sinusoidal voltages presentin the selsyn transmitterthe sinusoidal primary voltage and at least two sinusoidal secondary voltages-are supplied to an arrangement for producing recurrent series of pulses with intermediate pulse spacings corresponding to respective spacings of the three alternating voltages, each pulse series being representative of the instantaneous magnituds and polarities of the selsyn transmitter voltages and the recurrent frequency being many times higher than the frequency of the alternating voltage excitation supplied to the selsyn transmitter.

A combining circuit arrangement is provided for receiving the output voltages from the pulse time modulation converter and also for receiving the video output signals from the radar receiver and the trigger pulses from the radar transmitter and for supplying to a radio frequency transmitter a composite modulation wave representing all of these signals in a way susceptible of unambiguous component separation.

At the remote indicating station a radio frequency receiver is provided, and its detected output wave is supplied to separating circuit apparatus arranged to divide the composite `demodulation wave into video signals and trigger pulses' and a series of pulses resembling those provided in the transmitting station'pulse time converter. A reconverter system `receives the lastfnamed recurrent series of pulses and reconstructs plural sinusoidal voltage waves corresponding `to those produced by the selsyn transmitter at the radar scan arrangement, and these .i

. harmonic frequency.

af Fig. 6;

:as-reyesY 3 reconstructed voltage waves are' employed for controlling the azimuth input circuits of the remote radar indicator. For reasons which will subsequently appear more fully, the pulse time converter is made to operate at a pulse series recurrence frequency of the same `order of magnitude as the radar pulse repetitionV rate, but neither synchronous therewith nor at a simple harmonic or sub- An `important feature realized' through this arrangement is the interchangeability of local and remote indicator radar units so that no special constructional features are required in either one of these units, and the units are readily interchangeable for test or comparison Vpurposes.

yThe above objects and advantages will be made more fully apparent, and further features will be brought out tions per minute, forexample.

'4 rotation of the antenna-at a rate which may be 6 revolu- A selsyn transmitter V101 is coupled to the antenna system 23, as through aY 1:1 ratio spur gear 33. This selsyn transmitter receives primary circuit energization from a source 35, such as a generator of 60 cycles per second sinusoidal voltage, and provides a plurality of output alternating voltages between diiferent pairs of the plural conductors 37.

A radar presentation apparatus 39 is arranged to receive the input and output voltages of the selsyn transmitter 101 for azimuth sweep direction control of a cathode ray oscilloscopeV 41 therein, and to receive trigger Ypulses from the synchronizing oscillator of the transin the following detailed description of an embodiment of the present invention. In the drawings,

Fig. l is a general system representation showing theVV f c Fig". 3 represents, partly in block form, a coder and associatedrapparatus for use at the transmitting end of a teledata system in accordance with the present invention;

Fig. 4 shows graphically, to a common time base, the type of signals developed at various points in the coder of Fig. 3; Y- Y Y Fig. 5 is a schematic .circuit diagram ofthe portion of the coder of Fig. 3 represented by blocks 11S-25,27

and 28; Y

Fig. 6 represents, partly in block form, a decoder and associated apparatus-foruse at the receiving end of a teledata system according to the present invention;

Figs. 7 and 8 show graphically the type of signals developed at various points in the decoder of Fig.A 6; i

Fig. 9 is a schematic circuit diagram of the .decoder Fig. 10 is a schematicv circuit diagram ofthe signalcombining arrangements in accordance with the present invention; Y

Fig. 11 shows graphically the composite wave appearing at the output of the circuit of Fig.. l0; and

Figc. 12 is a schematic circuit Vdiagram of the signalseparatingarrangement. Y

VReferring particularly to Fig. l, a radar transmitterreceiver/system ofthe plan position indicator type is indicated 4at 21, the transmitter part being indicated as housed in the left-hand section of this unit 21 and the receiver part being housed in the right section.

A A` highly directive antenna 23 which may employ a paraboloidal Vreflector' 25 is supported on a rotatable column 27 which The transmitter includesa pulse generator .and a radiofrequency carrier wave transmitter responsive thereto for generating `very high intensity output pulses of extremely short duration, e. -g. for producing pulses of several kilowatts `peak power andof duration of the order of` a microsecond, the pulse repetitionrate being of theorder of 1000 pulsesper` second, ,for example.

The receiver may include a superheterodyne receiving circuit; `and unit 21 may further include a transmitting-` .receiving radio-frequency switching' means ,such as the Well known T.-R box.

i i. A motor 29 is coupled tothe antenna system 23'through i alspee-dreduction gear train"31 forproducing continuous mitter section of unit 21, and to receive the video output of the receiver part of this unit, ,to produce a map of the locations of energy reilecting objects, theinternal arrangements of unit 39 may take any of a variety of well known forms, van illustrative arrangement for this Ypurpose `being set out in Fig. 2, and being described f subsequently inreference thereto;

A radio frequency transmitter 45 coupled through` a radio frequency output-conduit 47 to a `directive antenna 49 is employed to provide eilicient transmission of radio frequency energy to areceiver system including a further directive antenna 51, a radio frequency conduit 53, and a radio frequency receiver 55 tuned to the frequency of the transmitter 45.

The radio frequency output of transmitter 45 is modulated according to a composite wave (illustrated in Fig. 11) produced in the output circuit of the combining unit 57, which has one input circuit coupled to the video output terminals of the receiver part of unit 21 and another input circuit coupled to the trigger pulseterminals of the transmitter part of radar unit 21. Yet another input circuit oftheY combining unit 57 is supplied with recurrent series of output pulses from unit 59.` This unit 59 is arranged to generate reference pulses Vand variably spaced signal-representing pulses and "to control the time intervals thereamong according to simultaneous values of the several voltages in transmitter 101 taken at very short intervals throughout the .period of the excitation wave from generator 35, e. g. at intervals of 1,4300 second. 4 Y Y A separator 't 61 is Yarranged to receive the de- .modulated output receiver 55 and to provide .separate output components in three diierent output circuits corresponding to the separate input components of the` combining circuit 57. The reproduced video and trigger pulse output components Vprovided through unit 61 are i supplied to the video and range sweep. synchronization terminals of a remote indicator `39' which may be a vduplicate of unit 39 in the'transmitter equipment. The

output component of unit 61 corresponding to the pulse arranged for VVreconstructing plural sinusoidal. voltages corresponding exactly Vin relative strength and phase with the input. voltages of` unit 59.V These output voltages may be employed foractuating a selsyn repeater 237 arranged to rotate a pointer at all times in synchronism with the azimuth direction of the antenna system 23.

-`trigger pulses generated in the transmitter.

-receiver or repeater unit 71 is arranged to rotate the finto a cylindrical casing 65. The magnetic deection y coils in this casing 65 Ymay be connected through slip rings 67`and cooperating brushes to the output circuit of a sawtooth current V Wave generator 6,9 arranged with a synchronization pulsefinput circuit for receiving the A selsyn magnetic deflection yoke in synchronism with the rotationofthe`.antenna 23,` so that the direction of radial ydei@una@Uhr asiltarope waterway changes in synchronsm with the antenna rotation, and hence, the angular positions of vsignal images correspond to the azimuth angle directions in space of the energy reflecting objects.

The video signals from the radar receiver are supplied to video input terminals of unit 39, and thence through a 'coupling capacitor 73 to the control grid circuit of the cathode ray oscilloscope 41. Filament heating power Yfor this oscilloscope is supplied by a low voltage alternating current or direct current output circuit of a suitable power supply 75, and the grid and anode and focussing electrode voltages for the tube 41 are supplied from voltage divider circuits across a very high voltage direct current supply circuit of the power supply 75. A potentiometer 79 is connected in the output circuit of power supply 75, and its movable tap 77 is adjusted to bias the control grid of the oscilloscope 41 approximately to beam cut-olf bias voltage, so that contrasting brightly illurnin'ated areas are produced upon the screen of tube 41 by the positive voltage excursions in the video signals supplied from the receiver part of unit 21.

Returning now to Fig. l, it will be apparent that where indication only at a central station is desired to be produced according to radar scanners distributed at selected distant points, the oscilloscope unit 39 may be dispensed with in the radar pulse transmitting-receiving station, indicator 39, only being employed at the central station. Of course, even in such arrangements, an oscilloscope unit 39 may be provided at the stations and may be permitted to run continuously, or may be arranged to be switched on only when local test work is to be conducted; or provisions may be made for conveniently connecting a portable version of indicator 39 when necessary for special Vlocal tests or for servicing of the radar scanning station.

The details of the pulse time converter 59 areV set lforth in connection with Figs. 3 and 5 of the drawings `and those of the sinusoidal wave reconstructing apparatus 63 are set forth in Figs. 6 and 9.` These two units are Valso shown and separately claimed in my copending application Serial No. 710,781, tiled November 19, 19,46.

The details of the combining circuit apparatus 57 are 'shown in Fig. 10, and those of the separating circuit lapparatus 61 are shown in Fig. 12, and these units per se are claimed in my copending application Serial No. 738,055, tiled March 29, 1947, now Patent No. 2,570,249, issued AOctober 9, 1951.

Referring to Fig. 3 there is shown a selsyn transformer :101 having a rotor winding L102 and three stator windings 103, 104 and 105. Rotor winding 102 is connected `to a pair 'of terminals 106 which in turn may be connected to any suitable source of alternating current, not shown. Terminals 106 are also connected to the primary winding 107 of a transformer 108 having a secondary winding 109.

Stator windings 103, 104 and 105 are shown as being -Y-connected, the open end of winding 103 being connected to terminal 110, that of winding 104 being connected to terminal 111, and the open end of winding 105 being grounded. Terminal 112 is connected to one side of secondary winding 109 of transformer 108, the other side of this winding being grounded.

Terminals 11:0, 111 and 112 are connected respectively Vto electronic switches 113, 114 and 115. Each of these switches has associated with it and is actuated by a gate, these gates being designated respectively 116, 117 and 118. The outputs from switches 113, 114and 115 are connected together and to coincidence blocking yoscillator' 119.

A master blocking oscillator 120 is provided `and Ione `of `its outputs is supplied to gate 116. Gate 116 is connected to gate 117, and gate 117 in turn is `connected to .'-gate 118. p

@ne-of the outputs `of coincidence blocking oscillator M9 lisrsupplied to off-ltrigger generator 121, .the .output 6 of which in turn is supplied to each of gates 116, 117 and 118.

Another of the outputs coincidence blocking oscillator 119 is supplied to data blocking oscillator 122, which is also supplied with an output of master blocking oscillator 120. Another output of master blocking oscillator 120 is supplied to reference blocking oscillator 123.

The outputs of blocking oscillators 122 and 123 are furnished to and combined in a collector cathode follower unit 124, the single output of which is supplied through output cathode follower unit 125 to output terminal 126 and also to reset cathode follower unit 127. The output of the latter unit is supplied to sawtooth generator 128, the output of which is supplied to coincidence blocking oscillator 119. The output wave of generator 128 may be of any suitable form, as for example, a rising exponential function of time. i

In operation, when an alternating voltage is applied to terminals 106 three alternating voltages are present at terminals 110, 111 and 112 with respect to ground, the amplitudes of these voltages depending upon the position of rotor winding 102 with respect to stator windings 103, 104 and 105. In accordance with the present invention, each of these three voltages is sampled many times per cycle and used to determine the displacement in time of a pulse which appears at output terminal 126.

Let it first be assumed that master blocking oscillator 120 is in operation at the desired repetition rate, as for example 1350 cycles per second. This oscillator is so constructed that there isa definite time interval between the leading and trailing edges of each output pulse, as for example 8 microseconds. The output wave is represented by curve 131 of Fig. 4.

The leading edge of each pulse from master blocking oscillator 120 actuates data blocking oscillator 122 to produce a pulse represented by pulses 132:1 and 132b of curve 132 inFig. 4. Each of these pulses is supplied to collector cathode follower unit 124 and, after passing through output cathode follower unit 125, becomes the first pulse of a synchronizing doublet. In addition, each pulse from collector cathode follower unit 124 is supplied to reset cathode follower unit 127, which in turn serves to reset sawtooth generator 128, as indicated by portions 133e of curve 133 in Fig. 4.

The trailing edge of each pulse from master blocking oscillator 1.20 actuates referencerblocking oscillator 123 to produce `a corresponding pulse, shown in curve 134 of Fig. `4, which is supplied to'collector cathode follower unit 124. After passing through output cathode follower unit 125, each of these pulses becomes the second pulse of a synchronizing doublet appearing at Voutput terminal 126. The same pulse at the output of collector cathode follower unit 124 is also supplied to reset cathode follower unit 127, which again resets sawtooth generator 128, the latter unit thereafter presenting a rising sawtooth wave to coincide blocking oscillator 119, `as indicated by portions 133b of curve 133.

The trailing edge of each pulse from master blocking oscillator 120 opens gate 116, which in vturn renders switch 113 conductive. This permits the voltage between terminal 110 and ground to be supplied to coincidence blocking oscillator 119, in which it is combined with the output voltage of sawtooth generator 128. When the sum of these two voltages exceeds a predetermined value, coincidence blocking oscillator 119 is tripped to produce pulse 135a of curve 135. The `output of coincidence blocking oscillator A1119 actuates `off-trigger generator 121, the `output of which, indicated by curve 136, is supplied to gate 116 to cause this gate to close. This renders switch 113 non-conductive and the sampling of the voltage at terminal 110 lis thus completed.

The action of lcoincidence blocking oscillator 119whiclr causes "the closing of agate 116, in the manner just described, actuates data iblocking oscillator 1122, `causing uit to .produce a pulse :which is indicated by pulse 132cm curve` 132.` This pulse, `after passing through collector cathode following unit 124 andoutput cathode follower unit 125, forms a first Aintelligence pulse at output Yterminal 126. The same output of collector cathode follower unit 124 also actuates reset cathode follower unit 127, which in turn resets sawtooth generator 128 as before, and a newV sawtooth wave begins to rise at the input to coincidence blocking oscillator 119, as indicated by portion 133e of curve 133. f y

The closing of gate116 causes gate 117 to open, render- Ving switch 114 conductive and thus permitting the voltage at terminal 111 to reach coincidence blocking oscillator 119. Once again, off-trigger generator 121 is actuated as soon as the sum of the voltage at terminal 111 and the output voltage of `sawtooth generator128 exceeds a given value, turning gate 117 off and rendering switch 114 nongenerator 128 alone is never suicient to cause it to fire.V

The gating voltages `developed respectively by gates 116, 117 and 118 are shown by curves 137, 138 and 1739 of Fig. 4. The series of pulses appearingV at Voutput ter- `minal 126 is represented by curve 140, and will be seen put potential of sawtooth'generator`128. When both of Y the latter two potentials are? present, however, control swing type.

to comprise a synchronizing doublet consisting of pulses t 140a and 140b followed by intelligence pulses 140C, 140d and 140e. The value of the Yvoltage between terminal 110 and ground is represented by the spacing in time t between the second pulse 140b of the synchronizing doublet and intelligence pulse 140e.` The time interval between intelligence pulses 140C and 140d corresponds with the voltage between terminal 111 and ground. The

Vvoltage between terminal 112 and ground is represented electrode 51 reaches such a potential relative to cathode 211 that coincidence blocking oscillator 119 trips or tires and produces a pulse at theY secondary winding of output transformer 156. The manner in which the tiring of coincidence blocking oscillator 119 acts upon switches 113,114 and 115 (Fig. 3) will be explained later.

Master blocking oscillator 120 (Fig. 3) comprises the left-hand portion of vacuum tube 152, and is of the single- Its grid-circuit time constant is adjusted by means of rheostat 157 to obtain the `desired repetition rate, as for example 1350 cycles per second. An inductance coil 158 is connected between cathode 1759 and ground, its purpose being so toA lengthen the positive half of the grid cycle that its leading edge may be used to place the lirst pulse (140a in Fig. 4) of the synchronizing doublet, and its trailing Vedge toplace the secondrpulse Y 140b of the'doublet (Fig. 4) a desired interval later, as

for example 8 microseconds.V The voltage developed at control electrode 160 o master blocking oscillator 120 is amplified and inverted by the left-hand portion of vacuum tube 161, the output voltage of which is -applied `to anode` 162 `of the righthand portion of vacuum tube 163, which functions as data blocking oscillator 1,22 (Fig. 3). This output voltage is `also applied to a differentiating network comprising capacitor 164'and resistors 165 and 166.V Resistors 165 and 166 are connected in series between groundand the negative terminalrof potential source167, the positive terminal of, which is grounded. The junction of resistors 165 and 166, to which capacitor 1764 connects, is also connected to control electrode 168 of the lefthand portion of vacuum tube 163 which functions as reference blocking oscillator 123 of Fig. 3. Since a blocking oscillator may bc triggered by a positive pulse applied to its control electrode or with a negative pulse applied to its anode, it is apparent that data blocking oscillator 122 which constitutes a portion of a voltage divider also com- Y prising a rheostat 142 and resistors 143 and 144 in series. The` open terminal of rheostat 142 is connected to the positive 4terminal of potential Source 145, thefnegative terminal of which is grounded, andthe junction of resistors 143 and 144 is connected to control electrode 146 of Y the right-hand-portion of vacuum tube 147,1 which is arranged as a cathode follower with a load resistor 148. The junction of resistors 143 Vand 144 is'also connected `to anode 149 of the left-hand portion of vacuum tube -ineans of resistor 150, to control electrode 151`of the righthand `portion of `vacuum tube 152, which functions as the coincidence blocking oscillator 119 of Fig. 3. `Also applied to control electrode 151, through resistor 153,is the output voltageof sawtooth generator 128of Fig. 3, comprising'vacuum tube V154.` The time constantofthis genferator is adjusted to a desired value, as for example 90 microseconds, by means of trimmer capacitor 155. Cathwill iire at a time corresponding to the rise of the iirst half ,of the grid cycle of master blocking oscillator 120, and'reference blocking `oscillator 123 will lire with the fall ofthe same Vfirst half grid cycle.`

VVacuum tube 169 functions as collector` cathode `follower 124 (Fig. 3). Control electrode 170 is connected, through resistor 171, Vto the grid circuit of reference blocking oscillator 123; and control electrode 172, through resistor 173, connects to the input circuit of data Vblocking oscillator 122. Since cathodes 174 and 175 are connected'together and grounded through common load resistor 176, vacuum tube 169 functions to combine or add `the pulses from both oscillators. When both oscillators are resting, cathodes 174 and 175 are at a small positive potential. The firing of either oscillator causes, first, an increase in its grid potential which appears at cathodes 174-and 175 as a positive voltage, and second, a decrease t in its grid potential below cut-ol of vacuum tube 169.

trode 177 of the right-hand portion of vacuum tube 178,

which functions as output cathode follower having output terminal 126Y (Fig. 3).

The left-'hand portion of vacuum tube 173 serves as reset cathode follower 127 of Fig. 3. Its control elec-` trode 179 is coupled tocontrolV electrode 1 77 of output Ycathode follower 125 by means of capacitor 180, so that positive pulses appearing at output terminal 126 are re- Y producedfat cathode 181,` which in turn is coupled by ode 211 of vacuum tube 152 is connected-to the junction t of resistors 212 and 213 inseries Aacross potential source '145, so that it is maintained at a positive potentiall higher than either that developed across resistor 148 or the outcapacitor 182 to control electrode 183 of the left-hand portion of vacuum tube 154. This tube functionsY as saw-A tooth kgenerator 128 (Fig. 3).: Anode 184 is connected estarse 9 of resistor 185, and is by-passed to ground by capacitors 155 and 186 in parallel. Reset pulses applied through capacitor 182 drive control elsctrode 183 heavily positive, thereby throughly discharging capacitors 155 and 186 and momentarily reducing the potential of anode 184 to a value closely approaching zero. Thus the sawtooth generator is reset.

After resetting, control electrode 183 returns to a high negative value, beyond the cut-olf value of the tube, and the potential of anode 184 rises exponentially and unimpeded towards the potential of source 145. This negative bias voltage is maintained by grid-circuit rectification which takes place during the resetting pulses. The

right-hand portion of vacuum tube 154 serves as a A cathode follower to reproduce, across its output resistor V187, the sawtoothvoltage developed at anode 184.

Vacuum tube 188 functions as gate 110 (Fig. 3). This tube is connected in an Eccles-Jordan trigger circuit, so that current ows in only 'one portion of the tube at a time. A negative pulse applied to one control electrode causes the Vcorresponding portion of the tube to become nonconductive and the other `portion conductive, and vice versa. Control electrode 189 of the left-hand portion of vacuum tube 188 is directly connected to control electrode 190 of the left-hand portion of switching vacuum tube 147, and the common connection is coupled by means of resistor 191 and capacitor 192 tothe input circuit of the left-hand portion of vacuum tube 152, which functions as master blocking oscillator 120 (Fig. 3). When a negative voltage pulse is applied through capaciter 192, control electrodes 189 and 190 become negative with respect to ground, so that the left-hand portion of v'acuurn tube 147 is cut off. This permits the righthand portion of Vacuum tube 147, which functions as a cathode follower, to conduct, so thatthe switch is effectively closed or conductive. When a negative voltage pulse is applied to control electrode 193 of the right-hand portion of vacuum tube 188, in a manner to be described subsequently, control electrode 189 rises to a small positive voltage relative to ground, causing control electrode 190 to go positive and the left-hand 'portion of vacuum tube 147 to become conductive, so that the switch is effectively open or non-conductive.

The right-hand portion of vacuum tube 161 functions as the off-trigger generator 121 of Fig. 3. Its control 'electrode 194 is coupled by means of capacitor 93 to the input circuit of coincidence blocking oscillator 119, so that a positive pulse is applied to electrode 194 when the oscillator fires at the end of a sampling process. The right-hand `portion of vacuum tube 161 inverts and am- -plifes this pulse, the resultant negative pulsebeing supplied to control electrode 1930f vacuum tube 188 by means of capacitor 195, and to anode 162 of vacuum tube `163 through capacitor 196.

All the apparatus directly associated with the channel supplied by terminal 110 has now been discussed. Vacuum tubes 197 and 198 serve as switches 114, 115 of lFig. 3, in a manner similar to that described in connection with vacuum tube 147, the right-hand portions of these three tubes having common cathode resistor 14S. Likewise, vacuum tubes 199 and 200, functioning as `gates V117 and 118 (Fig.` 3) are analogous, with respect to ter- `negative voltage pulse is applied 'to control electrode 193 through capacitor 195, gate 116 is turned off and anode 202 of vacuum tube 188 falls in potential. This produces a negative pulse on control electrde12`01, `turning gate "117 on after a delay of a few microseconds due to reu10 sister 2'04. u When gate 117 in turn is turned olf by a negative pulse through capacitor 209, the fall in potential at anode 206 'turns on gate .118 after a small delay interval due to resistor 208. When gate 118 is turned off by a negative pulse lthrough capacitor 210, all the gates remain olf.

A complete xsecpience of the coding operation will now be described, reference being made to Figs. 3, 4 and 5 of the drawings. The cycle starts when the leading edge of the output pulse (curve 131) of master blocking oscillator120 triggers data blocking oscillator 122, forming lfirst pulse 140a of the synchronizing doublet. Data blocking oscillator 122 resets sawtoo'th generator 128 by `means of collector cathode follower 124 and reset cathode follower 127 (portion 133a of curve 133).

After a predetermined interval, as for example 8 microseconds, the trailing edge of the output pulse (curve 131) of master 'blocking oscillator 120 triggers reference blocking oscillator 123 forming second pulse 1'40b of the synchronizing doublet. The output of master blocking oscillator 120 is differentiated by elements 191, 192 and 214, and applied to controlfelectrode 189 of gate 116. This in turn opens gate 116 (curve 137) and renders switch 113 conductive so that the voltage at input terminal 110 is sampled. In the meantime, the output voltage (curve 133) of sawtooth generator 128 has risen slightly. Reference blocking oscillator 123 resets sawto'oth generator 12'8 to zero again by means of collector cathode follower 124 and reset cathode follower 127.

The eutput voltage of sawtooth generator 128 again rises (portion 133b of curve 133) until 4the total voltage between control electrode 151 of vacuum tube 152, compris'ing `coincidence blocking oscillator 119, and ground 'reaches apredeterrnined value, as for example 143 volts.

The time interval required to reach this value depends upon the instantaneous voltage being sampled at terminal 11'0, and may for example vary from 20 to 142 microseconds. Coincidence blocking oscillator 119 fires, producing an eff-trigger voltage pulse (curve 136) through off-trigger `"generator 121, and intelligence pulse 140e by means of data blocking oscillator 122, collector cathode follower 124, and output cathode follower 125. Thus intelligence pulse 140e` follows second synchronizing 'pulse `14012 by a time interval Whose duration is a function of the instantaneous voltage at terminal 110, Gate 116 (curve 137) is turned olf by the off-trigger voltage (curve 136), thereby rendering switch 113 non-conductive and bringing to an end the sampling of the voltage at terminal 110. Very shortly after gate 1156 is turned off, gate 117 (curve 138) is turned on, thus rendering switch 114 conductive and-permitting the sampling `of the voltage at terminal 111 to begin. Sawtooth generator 128` is "reset to Zero by data blocking oscillator 122 through collector cathode follower 124 and reset cath ode follower 127. y

Once again, the output voltage of sawtooth generator 4128 rises (portion 133e Vof curve 133) until the total voltage at control electrode 151 reaches the above-mentioned predetermined value. The, time interval required to reach this value is dependent *upon the instantaneous voltage being sainpled 4at terminal 111, land may for example `vary from 20 tov 142 microseconds. Coincidence blocking bscillator 119 fires, producing `an off-trigger voit- Aage pulse (curve 136) through off-trigger generator `121,

and intelligence Vpulse 140d by means of data blocking oscillator 122, collector cathode follower 124, and output cathode follower 125. Intelligence pulses 140C and 140d are thus separated by a time interval whose duration is a `function of the instantaneous voltage at terminal 1111. Gate 117 (curve 136) is turned off by the off-trigger voltage (curve 136), so that switch 114 is rendered non-conductive andthe sampling of the voltage atfterininal 111 ended. Almost immediately after gate 1 17 is turned oit, gate 118 (curve 139) is, turned on, so

that switch 115 becomes conductive and the sampling of `the voltage at terminal 112 is permitted to begin. Sawtooth generator 128 is reset to'zero by data blocking oscillator 122 through collector cathode follower 124 and reset cathode follower 127. l

Once again, the output voltage of sawtooth generator 128 rises (portion 133d of curve 133) until the total voltage at control electrode 151 reaches lthe above-mentioned predetermined value. The time interval required to reach this value is dependent upon the instantaneous voltage being sampled at terminal 112, and may for example vary from 1l to203 microseconds. (The range here given by way of example is different from that given above in connection with the sampling of the voltages at .terminals 110 and 111 since, in the arrangement shown in Fig. 3, the peak'valu'e ofthe reference voltage devel-Y oped ,across winding'109 of transformer 108 may exceed the peak value of the voltages applied respectively to terminals 110 and 111.) Coincidence blocking oscillator 119 lires, producing an oE-trigger voltage pulse .(curve 136) through off-trigger generator 121, and intelligence pulse 140e, by means of data blocking oscillator 122, collector cathode follower 124 and output cathode follower 125. Thus intelligence pulse 140e follows intelligence pulse 140d by atime interval whose duration is a function of the instantaneous .voltage at terminal 112. l

Gate 118 (curve 138) is turned olf by the olf-trigger voltage (curve 136), so that switch 115 is rendered nonconductive and the sampling of the voltage at terminal 112 ended. `The outputY voltage of sawtooth generator 128 continues to rise and would reach a high value, as for example 250 volts, after a long interval of time. However, since no switch `is conductive at this time, this voltage is insuicient to cause the coincidence blocking oscillator to re. After gate 118 is turned olf and switch 115 thus rendered non-conductive, alljthe gates remain turned oif andV all the switches remain non-conductive until the next sampling cycle is started. It is important to note that, following a circuit disturbance, as for example a momentary interruption of power, only one sampling cycle is required toV restore an improper gate or switch condition to normal. Y i

Fig. 6 is a block diagram ofthe decoder and associated apparatus. Input signals, from the coder of Figs. 3 and 5, are applied to input terminal 215 and pass through azi- 'Y muth separator unit 216. The output of this unit comprises a series of pulses ysuch as shown Yby curve 350 of Fig. 7. These pulses are supplied to reset blocking oscillator 217, which `in turn actuates olf-triggerpulse former 218 and furnishes positive trigger voltages to sawtooth generator 219. i

220, 221 and 222 having associated with them switches 223, 224 and 225, respectively. (The latter six units are similar respectively to units 116, 117, 118, 113, 114 and 115 of the `coder of Fig.` 3.) `The output of unit 218 is also supplied to synchronizing `gate 226 and to syn- .chronizing switch 227.

Sawtooth generator 21,9 hasan output waveform (curve 352, Fig. 7p) which is `substantiallythe same function i vof time as is that of sawtooth generator 128 (Fig. 3) of This output is supplied to evaluators228, 229

transformer 237 is provided, having and 241. The stator windings are shown as being Yeconnected, the.v open end of winding 239beingconnected to theoutputAA of unit 2,34, that offwinding `240 to the output unit 2345,'a`nd .the ,open end of winding 241V cycle.

being grounded. The output of unit 236 is connected to one side of primary winding 242 of a transformer 243, the other side being grounded. Secondary winding 244 of transformer 243 is connected to rotor winding 238.v

In operation, synchronizing gate 226 and synchronizing switch 227 are actuated by the first two pulses (356:1 and.350b in Fig. 7) of each sampling cycle comprising the synchronizing doublet, and prepare for operation gates 220, 221 and 222 by closing any one of these gates which happens to be open. pulse also resets sawtooth generator 219, which has a decay time less than the time interval between the synchronizing pulses, as shown by portions 35211 of curve 352 in Fig. 7. Succeeding intelligence pulses (350e,` 350d and 350e of Fig. 7) reset sawtooth generator 219, in each instance after its output voltage has built up to a value dependent upon the time interval which has,`

elapsed since the preceding pulse occurred.

Gate 220 is opened by thesecond synchronizing pulse (350Z: in Fig. 7) and remains openuntil the rst intelligence pulseV (350e in Fig. 7) lires reset blocking `oscillator 217, causing olf-trigger pulse former 218 to produce a negative pulse which closes gate 220. When gate 220 closes, gate 221 is caused to open. It remains open until closed by the occurrence of the second intelligence pulse (350d inFig. 7). VThis closes gate 221 and opens gate V222. 'The latter gate is closed by the third intelligence pulse (350e in Fig. 7), and all the gates nowV are closed and remain closed until gate 220 is again opened by the synchronizing doublet of the next sampling The operation of these gates is shown graphically by curves 354, 355 and 356, respectively, of Fig. 7.

When any of gates 220,' 221'and 222 is open, as described above, the corresponding one of switches `223,

224 and 225 is rendered conductive. This in turn causes the corresponding one of evaluators 228, 229 and 230 to be connected to theV output Aof sawtooth generator Y consists of successive peaks of the interrupted sawtooth .V p A Off-trigger pulse former 21S provides negativertrigger. voltages (curve 351, Fig. 7), which are supplied to gates voltage (curve 356, Fig. 8)V and contains, as a fundamental component obtained by filtering, a duplicate (curve 357, Fig. 8) of the voltage applied to terminal 110, in Fig. 3. Y

Since the voltages developed at terminals 232 andy 233 are likewise duplicates, after filtering, of the voltages applied respectively to terminals 111 and 112 in Fig. 3, it will be readily apparent that the rotor of receiving selsyn transformer 237 Will reproduce the rotaa rotorfwinding 238 and three stator windings `239, 240

tionaladisplacements of the rotor of transmitting selsyn transformer 101 in Fig. 3. It will be equally obvious that the system of the present invention is not limited to the transmitting and reproductionof three selsyn voltages, in the manner here shown `and described by way,V of example, but may be employed with fully equivalent results to Vtransmit a plurality of voltages,regardless `of their source, and reproduce` them at` the receiving end with proper relative instantaneous values.

Reference is now made to Fig. 9, which shows, in schematic form, the circuit details ofV the decoder uof Fig. 6. InputA terminal 215 is connected to the control electrodes 245 of a vacuum tube 246, which functions as azimuthV separator 216 of Fig. `4( Tube 246 is so biased as to respond only to positive excursions applied to control electrode 245,'such signals rendering the tube conductive. Negative potentials applied tocontrol elec-` trode 245 haveno appreciable effect on the `operation Each synchronizing '0E-trigger pulse lead 256 throughhcapacitor 302, conduction is transferred to the left-hand portion and the synchronizing gate may be said to be turned on. The latter portion continues to conduct for an interval dependent upon the values of resistance and capacitance as synchronizing switch 227 (Fig. 6), functions as ay cathode follower. Its control electrode 303 is connected to the junction of resistors 304 and 305 which are connected in series between anode 306 of the left-hand portion of vacuum `tuhe 300 and the negative terminal of potential source 307, the positiveterminal of which is grounded. Thus, when-the left-hand portion of vacuum tube 300 is conducting, controlelectrode 303 becomes substantially negative relative to ground and cathodes 308 and 309, which are connected together, remain approximately at ground potential. Y Since control relectrode 263 of vacuum tube 262,` to which electrodes 266 and 267 of vacuum tube 268 are both directly connected, s normally substantially at ground potential, the diode comprised of the right-hand portion of vacuum tube 268 does not conduct and no negative pulse is developed and used to open gate 220 (Fig. 6). This is the situation after the occurrence of the lirst synchronizing pulse (350d Vin Fig. 7), but before the occurence of the second synchronizing pulse (350b in Fig. 7). Y

VCathodes 308 and 309 of vacuum tube 268 are coupled to oit-trigger pulse lead 256 by means of capacitor 310. The negative voltage pulse due to the second synchronizing pulse (350b in Fig.'7), therefore, is applied to Vcathodes 308 and 309, causing theright-hand portion of vacuum tube 268 to become conductive. Gate 220 (Fig. 6) is thereby turnedon, and electrodes 266 and 267 of the right-hand portion of vacuum tube 268 then become substantially negative relative` to ground.

After the occurrence of the second synchronizing pulseV (350]) in Fig. 7) but before the Vltirst intelligence pulse '(3500 in Fig. 7) occurs,synchronizing gate 226 (Fig. 6) Areturns to its steady-state condition,

This causes control electrode 303 of vacuum tube 26,8,V and hence cathodes 308 and 309, to assume a positivepotential with respect toground. VElectrodes V266 and 267, comprising theanode of the diode portion of vacuum tube 268, are substantially negative relative to ground. synchronizing switch 227 (Fig. 6) 'is therefore so biasedY that the terminals 406 vand 407. A resistor 408 is connected between control e1ectrode402 and ground. Cathode 409 of `vacuum tube 401 is grounded through resistor 410. Screen-grid 411 is connected to a source of suitable positive potential diagrammatically illustrated at 412, and suppressor-grid 413 is grounded.

The anode 414 of vacuum tube 401`is connected through a resistor 415 and an inductor 416 to a source of suitable positive potential indicated at 417. Anode 414 is also coupled, by means of capacitor 418, to thecontrol electrode 419 of second vacuum tube 420. A resistor 421 is connected between control electrode 19 and ground.

VCathode 422 of vacuum tube 420` is grounded through a resistor 423 shunted by a capacitor 424.- The screengrid 425 of vacuum Vtube 420 is connected to positive Vsource 412, and the suppressor-grid 426 is grounded.

The anode 427 of vacuum tube 420 is connected through a resistor 428 and an inductor 429 to positive potential source 417. Anode 427 is also coupled, by a Y capacitor 430, tothe control electrode 431 of a vacuum tube 432. Control electrode 431 is connected through ground through a potentiometer 437, `the movable arm 438 of which is connected to an output terminal 439,`

446 of Vvacuum `tube, 444is connected to the movable armV 447 of a potentiometer 448, which in turn is connegative pulse due to the rstintelligence pulse (350e 220 (Fig. 6), and broken line 360 representing the diode clipping potential.

The situation is similar just before the occurrence of the remaining intelligence pulses (350d and 350e in Fig. 7), so that these pulses are likewise without eect Thus it will be apparent that gate 220 can be opened, and the resultantvsequence ofV operations initiated, only by the occurrence `of a pair of pulses having `a predeterminedV maximum time-spacing. The sequence cannot bestarted by a single signal pulse,'nor by a pairof pulses having a tithe-spacing greater than the predetermined value.

Referring to Fig. l0, there is shown a video amplifier comprising a f rstvacuum tube 401, the `control electrode 402 of which is coupled by means of a capacitor 403 to nected in series with a resistor 449 between source 417 ,anode 452. The suppressor-grid 453 of vacuum tube V444 is grounded.

For the purpose ofV introducingV trigger signals, akpair of terminals 454 and 455 areprovided, the latter terminal beinggrounded. Terminal 454 is coupled by a capacitor 456 to the control electrode 457 of the lefthand portion of vacuum tube 458.k A resistor 459 is connected between control electrode 457 and ground. The cathode 460 is grounded. The anode 461 is connected through a resistor 462 to source 417, and is coupled by a capacitor 463 to the cathode 464 of the right-hand portion of vacuum tube 458. Cathode 464 is connected to ground by a resistor 465. The control electrode 466 and the anode 467 of the right-hand portion of vacuum tube 458 are'connected together and to cathode 4097`of vacuum tube 401.

A pair of terminals 468 and 469 are provided for the purpose of ,introducing the azimuth signal input, terminal Vtube Y472, Vcontrol. electrode 471 beingV connected by` a resistor 473 to a sourceof suitable negative potential indicated at 474. The cathode 475 is grounded, as is the suppressor-,grid 476. The screen-grid 477 is connected to source 417. The anode 47 8is connected through r a-resistor 479 to anode 427 of vacuumrtube 420.

In operation, the positive video signals which are applied to input-terminals 406 and 407 are amplified by: vacuum tubesV 401 and 420, the extent of this` amplification being controllable by the setting of the potentiometerY 405. Inductors 416 and 429 in `the anode circuits respectively of vacuum tubes 401 and420 serve asrpeaking choke coils.

The positive trigger signals are applied to terminals 454 and 455 and are shaped by vacuum tube 458. The positive trigger signal voltages charge capacitor 456, and this charge leaks olf exponentially throughresistor 459. Thus a trigger pulse having a steep leading edge and a sloped trailing edge is developed across resistor 462 and applied to diode cathode 464 by means of capacitor 463. If desired, capacitor 463 may be made adjustable and used as a trigger signal gain control. The output -of the trigger shaping circuit, which may for example comprise pulses having an amplitude of 40 volts, is mixed additively with the radar video signals in view of the connection from the diode anode (electrodes 466 and 467)` to cathode 409 of vacuum tube 401. The right-hand portion of vacuum tube 458 serves as a diode rectifier to prevent any negative radar video signals, which may be developed across resistor 410, from feeding back through the trigger shaping circuit.

The azimuth signal input is applied to terminals 468 and 469, and may comprise 150-volt positive pulses. Vacuum tube 472 is normally biased far below cut-olf, since its control electrode 471 is connected to negative potential source 474 having for example, a potential of 105 volts. When the positive azimuth pulses are applied through capacitor 470 to control electrode 471, however, vacuum tube 472 becomes conductive and a large current flows through resistors 428 and 479 in its ano-de circuit. Since resistor 428 is" common to the anode circuits of vacuum tubes 472`and 420, this large current ow through vacuum tube 472 causes anode 427 of vacuum tube 420 to change its potential with respect to ground in a negative direction. `Its potential may/,for example, become less positive by approximately 100 volts during each azimuth signal pulse.

The composite signal wave at the output of the video amplifier comprising vacuum tubes 401 and 420A is fed, by means of capacitor 430, to vacuum tube 432,.which is arranged to operate as a cathode follower. Cathode 436 of this vacuum tube is normally positive with respectto ground, as for example by 25 volts. Since the azimuth pulses always cause at least 60-volt negative excursions of anode 427, even when the radar trigger and azimuth pulses are coincident, the azimuth pulses will drive lcontrol electrode 431 sufficiently negative with respect to cathode 436 to cut olf vacuum tube 432. In this manner, the azimuth pulses take precedence over the video or trigger signals.`

The output of cathode follower vacuum tube l432 is developed across potentiometer 437, and a desired portion of it is chosen by the setting of movable arm 438 and appears between output terminals 439 and 440.

Vacuum tube 444 serves as a clipper, and has its control electrode 446 maintained at a desired positive potential relative to ground depending upon the setting of sliding arm 447 of-potention1eter`448. By suitably adjusting this positive potential, the extent of the negative excursions of cathode 445 due to the azimuth pulses may be limited to a desired value. Thus potentiometer 448 serves as an azimuth gain control.

The composite output wave developed between terminals 439 and 440 `(Figs. 1 and l0) is illustrated in Fig. ll. It includes high-intensity negative pulses corresponding to the pulses of wave 351 of Fig. 7, these pulses conveying a version of the output of the pulse `time converter 59 of Figs. 1, 3 and 5. The output wave of Fig. ll also includes very high intensity positive pulses 482, 482', 482 corresponding to the trigger pulses from the transmitter of radar unit 21 (Fig. l), these pulses lbeing in exact syn-` chronism with the radar pulse transmissions.

The composite wave of Fig. 11 yet'further inclu-des a video signal component of maximum intensity limited to the value represented by line 480, and appreciably lower than the intensities of the trigger pulses. This video component represents the intensity variations whichmust be effected in the cathode ray beam in the indicator as frequency being 1000 pulses per second. This frequency allows unambiguous indications of object distances up to approximately 90 miles. t

The period P of the pairs 600, 600', 600 of reference pulses extending in the negative direction (i. e., Ibelow dotted line 601) in Fig. 11 is of the same order of magnitude as that'of the period P of the radar trigger pulses, but is unequal thereto. Whereas 1000 trigger pulses may occur per second, the number of pairs per second of the reference pulses 600, 600', 600" from unit 59 must be different from the trigger pulse frequency and free from any simple harmonic relation therewith. For example, a frequency of 1350 reference pulse pairs per second may be provided by unit 59, so that the period P is 1/1350 second.

Fig. 11 illustrates the variation of the inter-pulse spact i ings of the negative pulses representing the input voltage andthe two output voltages of the selsyn transmitter 101. Spacing c represents an instantaneous value of the selsyn transmitter input voltage, andspacings a and b represent corresponding instantaneous Values of the first and second output voltage waves, respectively, from selsyn unit 101. It is apparent that in the successive instantaneous measurements of the voltage values at 174350 second intervals, the successive ones of intervals a, a', a" are increasing, those of b, b', b are decreasing, and those of c, c', c are increasing. Assuming a selsyn transmitter primary supply frequency of cycles per second, 221/2 sets of these measures are taken in each cycle with a frequency of unit 59 of 1350 cycles or pulse series per second.

`A study of the video signal pattern reveals three prominent peaks or pips inthe interval between trigger pulse 482 and the next trigger pulse 482', The tirst of these, designated 605, is at a position of approximately 150 microseconds delay, corresponding to a distance of an energy retiecting object of approximately 131/2 miles. The next of these peaks, 607, is at a time-position of 420 microseconds delay after pulse 482, and hence represents an object at approximately 38 miles distance. The third, designated 609, is at a position of approximately 720 microseconds delay, indicating presence of an energy reflecting object at a distance of approximately miles. Pip 605 is limited in intensity to the maximum video output intensity represented by line 480,through the limiting action in the radar receiver. This pip is relatively broad, and may represent the energy reected from the near side of a large hill or a very extensive object such` as a very large building, for example, the transmission paths to different parts thereof being of various` lengths within an appreciable range of distances.

Since the speed of rotation of antenna 23 is quite low, e. g. or" the order of 6 R. P. M. (36 per second), and since the pulse repetition rate is of the order of 1000 pulses per second, the pulse repetition rate expressed in terms of the speed of revolution of the antenna 23 may be said to be the quotient of 1000 and 36, or approximately 28 pulses per Adegree revolution of the antenna. Conversely, the antenna progresses .036 per radar pulse. Now, since the angular breadth ofthe directive pattern produced by the antenna 23 normally is of the order of 1 to 2, it will be apparent that an energy reflecting object in a given direction will be impinged" upon'by a series of many successive `radar pulses, and

will'produce acorresponding series of manyretlected` respectively. viewof Fig.1l, a still further pulse 60'5vrece1ved via `reflection from the nearest of these `three energy rellectl and receivedradar signals all delayed after the correspending transmitted pulses by a time `delay corresponding to the distance ofthe object. s l.

This is illustrated in Fig. 1l, wherein the three distinct energy reflecting objects represented by pulses `6115,

607 and 609 are similarly represented `by reflected pulses correspondingly displaced after the next transmitted pulse 482', these pulses being designated 605@ 607 and' 609 Near the extreme'right-haiiil-endV of the" ing objects is apparent. p Y.

The importance of makingunit 59 (Fig. l) to operate at a `different pulse seriesrepetition rate `from Vthe pulse repetition `rate of` the radar transmitter now becomes apparent from an inspection of Fig. 1l. In this illustration, one of the negative pulses 611 is noted to have interfered withpulse `6415 from the nearby object, splitting the broad positive pulse which normally should appear into two narrow pulses spaced by a very narrow time interval. A narrower pulse, such as pulse 609', upon coincidence with one of the negative pulses, would be entirelyv obliterated 'by the preferential response to the azimuthsignalling'pulses in combined unit57. lf this condition were repeated in several successive intervals betweenradar pulses, certain target indications would be lost, Vand thus, the radar picture would be seriously altered, rendering it unreliable.

Howeven'with the appreciable difference maintained between the radar pulse repetition rate and the repetition rate ofthe pulses-produced by unit 59, the occasions of p interference `of the negative pulses with the 'positive pulses `are made both infrequent and random. Considering the r25 `to 50successive pulsesV of. radar" energy which will impinge upon a givenreilecting objectV of finite area, in View `of the bearn width, antenna'rotationv speed, and pulse repetition rate as discussed above, by far the greater number of reilected pulses detected in the receiver partl of the radar unit 21 will be represented by intact video pulse wave portionsY in Vthe compositeV wave produced at the `output circuit of unit 59.

As an illustration of this, note that pulse 605 andpulse p 605.", pulses immediately preceding and immediately succeeding the `partially destroyed pulse 605:', are intact,

and are well removed from the respective nearest negafV ture produced on remote gindicator39 exactly duplicates that Vproduced on `unit 39 located' at the Aradio station, and there is no effect whatever discernible, on vthe'pface of indicator 39of'theoccasional interferences` suchas that illustrated at 611, `605 in' Fig. V11. Y v Referring now to l2, which isa schematic circuit diagramof the signal-separating arrangements `of the Y present invention, there is show n a video amplifier 560 having input terminals 501 and StZ,V the latter terminal being grounded. The ungrounded output Aterminal of video amplifier 500 is coupledfby meansrof a Vcapacitor 503 to thecontrol electrode Stli'of. a vacuum tube 505V.;

The screen-grid513V of vacuum tube `5%' is `connected to Vpositive potential source 417. The suppressor-grid 514 is connected to cathode 508. The anode '515 V.is connected through a resistor 516 Vto positive potential source i 417, andis coupled by means of capacitor 517 to the control electrode 5.18 of a vacuum tube 519. The resistor 520 is Vconnected between control electrode518 andV ground;

Thefcathode 521 of vacuum tube `519 is grounded. The screen-grid 522 is connected to the junction of resistors 523 and '524 connected inseries between positive potential source 417 and ground, and this electrode is by-passed to` ground by a capacitor 525. The suppressor-` grid 526 is grounded. The anode 527 is connected to an azimuthsignaloutputterrninal 52 8,"the other azimuth signal output terminal 529 being grounded. `The anode V527 is connected to anazimuth signal output terminal 528, the other azimuth signal output terminal 529 being grounded. p ,p

Cathode 5w of vacuum tube505 is coupledby a capacu it'or 53) to the control electrodel -of a vacuum tube 532.V Resistors 533 and 534 are Yconnected-in `series between control electrode 531 and negative .potential source 474. p. I

The cathode 5155Y of vacuum .tube532is` grounded, as is the suppressor-grid 536. The screen-grid 537A isconnected to positive potential source 417. ll`heauode'5.?i8

is connected to source 417 through a` resistor 539, and is coupled by a capacitor Sdu to the control electrode 541 of a Vacuumtube 542. A resistor ,543is connected between control electrode 54.1V andV ground. The cathode V544 is grounded, as is the suppressor-grid `545. Screengrid 546 is connected by a resistor 547 to the junction of afr'esistor 548 and a capacitor '549V connected in Aseries between potential source417 and ground.` The anode 550 is connected through an inductor 551 and a resistor 552 to the junction of resistors 547 and 54S.

Anode 550 is coupled by a capacitor 553 to the control electrode `554 of the left-hand `portion of a vacuum tube 555, a resistor 556 is being connected between this control electrode and ground. The anode 557 is connected to positive potential source 417.

The cathode 558 of the left-hand portion of vacuum tube 55 is connected to ground through a resistor 559 and is coupled by a capacitor 560 to the control electrode .561 of a thyratron 562.V Control electrode 561 is connected `by a resistor 563 to the movable arm of a poten-f` H tiometer 564, which in turn is connected in series with Vradar pulses and the azimuth pulse series, the radar pic-` Y Control electrode 504 is connected by means ot a resistor- 506 to a Vsource of negative potential 597 having, for example, a potential of Vthree Volts.

uThe cathode508 of vacuum tube 595 is connected through a Vresistor 509 to a video output terminal 510. l The other video output terminal511 istgrounded. .A resistor512is`connected between terminals 510 and 511.`

a resistor 565 between ground and negative. potential source 474. The cathode 566 of thyratron S62 is connected to ground through Va resistor 567; and is directly connected to a trigger signal output terminal 568, the

other trigger signal output terminal '569 being grounded. The anode 570 of thyr'atron 562 is connected through a resistor 571to positive potential source417. A series network comprising a resistor 572 and a capacitor 573 is connected between anode 570 and ground. Y

Y Cathode 558 of VtheV left-hand portion of vacuum tube 555 -is also coupled by a capacitor 574` to the `control Velectrode 575 of the right-hand portion of vacuum tube 555.-. Control electrode l575 is-connected to the junction of resistors S576 and 577 which are in turn Vconnected in series between ground and negative potential source 474. The cathode 4Sit'is grounded.

The Vanode 578 Vof the right-hand portion of vacuum p tube 555 is connected through a resistor 579 to positive l potential source'417, and is coupled, by a capacitor 580 Vto the control electrode 581 ofthe left-handportion of aV vacuum tube 582. A resistor 583 is connected between control electrode V581 and ground. The cathode 584is; grounded. The anode 585 is connected through `a resistor 586 to positive potential source/117, and is also connected by a resist0r587 shunted by a capacitor 588 to vacuum tube 582.

the `control electrode 589. ot the right-hand portion of Control electrode 589 is connected `bya resistor590 to negative potential source 474.` The cathode 591 is grounded. The anode 592 is connected to the junction of resistor 579 and capacitor S80. This junction is also connected by a resistor 593 to the junction of resistors 533 and 534, the latter junction being by-passed to ground by a capacitor 594. A voltmeter 595 may be connected between ground and the junction of resistors 533 and 534, as shown. p t

In operation, the input signal which is applied to terminals 501 and 502 comprises a composite wave having the general characteristics shown in Fig.` 11. Since video amplifier (20`is` assumed to have an even number `of stages, a similar composite waveis applied to control electrode 54 of vacuum tube 505. Thisvacuum tube operates as a` cathode follower, and its control electrode 504 has applied to it a suitable negative bias potential, as for example three volts. This'bias serves toY limit the azimuth pulses to a desired value, as for example 11 volts. The video signalvoutput appears across resistor 512 in the cathodecircuit'fof vacuum tube 505 and may be utilized at terminalsf510 and 511.

Resistor 516 in the anode circuit of vacuum tube S05 has no appreciable effect upon the operation of this tube asa cathode follower since, thetubebeing a pentode, its` anode current is determined largely by the potential applied to sceeen-grid S13. The negative azimuth pulses from video amplifier 500, however, cause the anode current of. vacuum tube 505 to be cut olf, thus producing positive excursions of anode 515 which may, for example have a magnitude of approximately `2() volts. These positive anode excursions are applied to control electrode 518 `of vacuum tube S19, which is so biased as to respond only to positive excursions. Suchsignals render the tube conductive, causing the azimuth pulse output to be developed between terminals 528 and 529.

The output of vacuum tube 505, -as developed across its cathode resistors 509 and 512, is applied to control electrode 531 `of vacuum tube 532, which functions as a trigger signal separator. Control electrode 531 is normally biased to a substantial negative value, as for example approximately 40 volts. This bias is suficient to cut on the tube for peak values of the radar video signal. The azimuth signal pulses are of negative polarity and hence have no effect upon vacuum tube 532. The trigger signal pulses are positiveV and have approximately double the amplitude of `the peak radar video signals. each trigger pulse overcomes `the normal `negative bias on control electrode, 531 and` renders `vacuum tube 532 conductive for the brief duration of.,each pulse.

The resultant negative anode swings are amplified by vacuum tube 542, which operates with zero bias on its control electrode 541.` The purpose of` series screen resistor 547 is to reduce the anode current of this vacuum p tube to a reasonable value. `Each negative trigger pulse from vacuum `tube 532` causes the anode current of `vacuum tube 542 to be cut off.` Inductor 551 in the Thus 50 and60 volts, areY appliedtocontrol electrode 554 of developed across resistor 567 -may be` `utilized `at trigger` output terminals 568 and 569."`These,pulses for example.

22 t may have a duration of `l microsecond atV 70 volts and one ampere. C

For the purpose of maintaining the positivetrigger pulses applied to control electrode 561 of thyratron 562 at a substantially constant level, a feedback loop is provided. The positive pulses developed across cathode resistor 559 associated with vacuum tube 555 are applied by means of capacitor 574 to control electrode 575 of the right-hand portion of vacuum tube 555. This electrode is normally held at a substantially negative potential, as for example approximately 66 volts, by the voltage divider comprising resistors 576 and 577. The right-hand portion of vacuum tubeASSS conducts on each positive trigger pulse which exceeds this bias potential, and the resultant negative voltage swings of anode 578 are employed to trigger a one-shot multivibrator comprising vacuum tube 582. The left-hand portion of thisvacuum tube is normally conducting so that its anode 585 has approximately the same potential as its control electrode 581. The right-hand portion of vacuum tube 582 is normally non-conducting. Y

When negative trigger pulses are received from `vacuum tube 555, control electrode 581 is rendered increasingly negative so that the left-hand `portion of vacuum tube 582 is cut ott". The resultant positive swings of anode 585 are fed through resistor 587 shunted by capacitor 588 to control electrode 589 of the right-hand portion of vacuum tube 582, thereby rendering this electrode less negative and causing the right-hand portion of the tube to become conductive. Anode 592 thereupon becomes decreasingly positive, and this negative voltage swing is applied through an integrating network comprising resistors `593 and 534 and capacitor 594 to control electrode 531 of vacuum tube.532. 'l Capacitor 594 is normally charged so that its ungrounded terminal is substantially negative with respect to ground, as for example by` 4() volts. The negative voltage swings of anode 592 increase the negative voltage on capacitor 594 and thus increase the negative bias which is applied to corn trol electrode 531 of vacuum tube 532.

Capacitor 594 is charged negatively at a slow exponential rate. This gradually increases the negative bias voltage on control electrode 531 of vacuum tube 532 until the pulse amplitude developed across cathode resistor 559 associa-ted with vacuum tube '555 is reduced to a desired value, as for example to less than 50 to 60 volts. When this condition is reached, the multivibrator comprising vacuum tube582 rests until itis triggeered by another pulse from anode 578 of vacuum tube 555. The charge and discharge of capacitor 594 occurs at a rate faster `than the amplitude variation of the radar trigger pulses, but less rapidly than the pulse repetition rate. In this manner, thev average pulse amplitude delivered at output terminals 568 and 569 remains essentially constant for a wide range of amplitudes for the input pulses cuit, is well within the firing range of the tube and hence introduces no difficulty.`

As pointed out above, the negative charge on capaci-7' itor 594 increases as a function of the amplitude of the trigger signal pulses applied by capacitor 530 to control electrode 531 of vacuum tube 532. Although these input pulses are of extremely short duration, it is evident that the voltage -across capacitor 594, as indicated by example by voltmeter 595, is closely proportion to the amplitude `of the input pulses. l

While there has been described what is at present considered the preferred embodiment of the invention, 'it will be obvious to those skilled in the art that various `changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in theappended claims to cover all `such changesand,` 

